Removal of Ni(II) ions from aqueous solutions using clinoptilolite: equilibrium, kinetic and thermodynamic studies

Abstract

In this study, clinoptilolite was characterised and used for the removal of Ni(II) from aqueous solutions. The effect of pH, adsorbent dosage, contact time and temperature on the adsorption process was studied in batch experiments. Kinetics data were best described by a pseudo-second-order model. The maximum uptake was 39.7 mg·g⁻¹. The adsorption data can be well described by the Langmuir isotherm. Thermodynamic studies indicated that the adsorption was spontaneous and exothermic in nature. The sorption energy calculated from the Dubinin–Radushkevich isotherm indicated that the removal of Ni(II) took place via an ion-exchange mechanism. FTIR spectra measured in the middle infrared showed that the ionic exchange in clinoptilolite causes a change in intensity of the band at ∼676 cm⁻¹, connected with pseudolattice vibrations of rings formed by AlO₄ and SiO₄ tetrahedra.

Keywords:

• clinoptilolite
• ion-exchange
• Langmuir isotherm
• Dubinin–Radushkevich model
• kinetics
• Ni(II)
• thermodynamic
• MIR spectra